Effect of potential variation on morphology and photoelectrochemical properties of TiO2 nanotube arrays (TNAs) by two-step anodization method

TNAs have been synthesized using a two-step anodization method by increasing the second-step voltages. The titanium (Ti) foil was used as the anode, and the first step of anodization layer was removed by sonication in the deionized water. The second anodization step was conducted using the same electrolyte but at a higher potential. The modification of the second-step voltage was discussed with correlation for the morphology and photoelectrochemical performance of TNAs. Increasing the second voltage of two-step anodization leads to a decrease in the bandgap of the anatase phase of TNAs at 3.09 eV. The highly ordered TNAs were formed by increasing the second-step voltage based on the Fast Fourier Transform (FFT) images with a higher regularity ratio (RR) with 30 V for 30 min in the first step and 40 V for 30 min in the second step. The tube length of TNAs was produced in a short time of anodization. The photocurrent density of TNAs prepared by increasing voltage in the second step is higher than that of the one-step anodization.